1. Field of the Invention
The present invention relates to battery monitoring circuitry and more particularly, to charging, monitoring and alarm circuitry to predict both degraded battery capacity and short life expectancy of a monitored battery.
2. Description of the Prior Art
In a standby power system, typically the back-up battery will not be used for extended periods of time. However, it is essential that the battery be capable of delivering sufficient energy to the load when required. Accordingly, it is important to monitor the battery to determine when the battery should be replaced.
Various arrangements and techniques are known for charging and testing batteries used for various applications. For example, U.S. Pat. No. 4,426,612 discloses a constant current battery charging and testing circuit for determining the state of charge of the battery by closing a switch to place a current sink across the battery, sensing the battery voltage and comparing the sensed voltage with a reference voltage.
U.S. Pat. No. 4,316,133 discloses a battery charging circuit for continuously charging a back-up battery. The charging circuit produces a charging current which is a function of both the temperature and the battery voltage. Testing is provided by placing a test load across the battery effectively removed from the charging circuit, sensing the battery voltage and comparing the sensed voltage with a reference voltage.
Typically, reliability of the battery is determined by such manual testing arrangements and/or by frequent periodic battery replacement. It is important to provide a battery monitoring arrangement that is automatic and that eliminates the need for manual intervention.